1. Field of the Invention
The present invention relates to an ink jet recording device which carries out recording by discharging ink from a recording unit onto a recording medium, and to a recording device which is used as an output device equipped with such functions, such as a fax machine, a copier, a printer, a multi-function device, a work station, or the like.
2. Description of the Related Art
The increase in popularity of color documents in offices in recent years has been remarkable, and various output devices therefor have been proposed. In particular, the ink jet method, which enables devices to be made compact and which is low cost, is used in various output devices.
A recording head used in the ink jet method is structured by an energy generating device, an energy converting device which converts the energy generated at the energy generating device into ink discharging force, an ink discharge opening from which ink drops are discharged by the ink discharging force, and an ink supply path which communicates with the ink discharge opening and supplies the ink. Examples of the energy generating device are devices using an electromechanical converting body such as a piezo element or the like, a device which forms an air bubble by heating the ink by an electrothermal converting element having a heat-generating resistor, and discharges an ink drop due to the formation of the air bubble, and the like.
In a recording head utilizing an electricity-heat converting element, because the electricity-heat converting element is compact, not only is it possible to dispose the ink discharge openings at a high density, but also, semiconductor integrated circuit manufacturing technology can be used as the technology for the manufacturing of the recording head. Therefore, a recording head provided with a large number of highly-precise ink discharge openings can be made to be compact, and can be manufactured at a low cost.
However, what is mainly popular these days is a printing method called serial scanning which carries out printing line-by-line by reciprocatingly moving a recording head while conveying a recording sheet. This method is compact and low cost, but has the disadvantage that the recording head must be scanned plural times in order to form an image over the entire sheet, and the printing speed is slow. In order to improve the printing speed, the number of scans must be reduced, and the recording head must be elongated. The technology which has pushed these features to their limits is a non-scanning printing system which carries out printing by a recording head disposed along the width of the sheet. This printing system is an ink jet recording device equipped with a recording head which corresponds to the width of the sheet and in which a large number of discharge openings are lined up along a length substantially equal to the width of the recording sheet. Recording is carried out by the recording sheet moving with respect to the recording head which is fixed.
In this way, in order to improve the printing speed and be able to handle application to use in the office, there has been proposed the ink jet recording device which, while continuously conveying a sheet, carries out printing by a non-scanning type recording head corresponding to the width of the sheet.
However, in the ink jet recording device, the conveyed state (e.g., fluctuations in speed) of the sheet below the recording head (the nozzle surface) greatly affects the printing performance. Accordingly, in a case in which a sheet is conveyed continuously, conveying the sheet stably at a constant speed is problematic.
To address this problem, structures have been proposed in which a sheet is conveyed in a state of being attracted to an electrostatically attracting belt or to an electrostatically attracting drum, and the sheet is conveyed at a constant speed (e.g., Japanese Patent Applications Laid-Open (JP-A) Nos. 2-179754 and 5-330030, which will be called Conventional Examples 1 and 2 hereinafter), and in which a sheet is conveyed while being nipped by two or more narrow belts for conveying and spurs (e.g., Japanese Patent Application Laid-Open (JP-A) No. 8-132700, which will be called Conventional Example 3 hereinafter).
On the other hand, in the ink jet recording device, poor discharging of ink drops arises and the image quality deteriorates due to dirtying of or ink drying at the nozzle surface of the recording head, and due to the generation of air bubbles in the ink flow path of the nozzle or the like, and the like. Thus, ink drops are discharged at times other than during printing (this is called “dummy jetting”), so as to prevent the ink from drying, and so as to remove dirt from the nozzle surface, and so as to discharge the air bubbles, which exist in the ink flow path, to the exterior together with the ink. Further, there is the need to provide a maintenance device which carries out maintenance such as wiping the nozzle surface to remove dirt from the nozzle surface and maintain the ink discharging performance, and the like.
Conventional Example 1 proposes a structure which carries out maintenance by a maintenance device abutting a recording head portion which is set in a posture different than that during printing.
In Conventional Example 2, an opening is provided at an electrostatically attracting drum, and a cap member, which receives the dummy jet, is disposed within the opening. Accordingly, when the sheet is conveyed (when printing is carried out), the sheet is conveyed by closing the opening. When dummy jetting is to be carried out, it is carried out by opening the opening. Further, wiping is carried out by wiping the entire head by a single blade.
Conventional Example 3 is a structure in which a recording head is raised from the printing position, and due to a maintenance device sliding, the maintenance device is positioned at a position facing the nozzle surface of the recording head, and maintenance is carried out.
When an electrostatically attracting method is employed as in Conventional Examples 1 and 2, the following problems arise. Because the force attracting the sheet depends on the electrical properties (the electrical resistance, the electrostatic capacity, i.e., the electrical conductivity, the dielectric constant, the thickness of the paper, and the like), the thickness and the type of paper which can be stably conveyed by electrostatic attraction are limited. Poor attraction may occur due to changes in the electrical properties of the sheet due to the printing (the adhesion of the ink) and due to fluctuations in the ambient temperature and humidity of the device.
Moreover, there are cases in which the locus of flying of the ink drop discharged from the nozzle is distorted due to effects of the attracting electrical field, and the printing is poor. In addition, there are cases in which an ink mist or dirt floating about due to the effects of the attracting electrical field adheres to the nozzle surface of the recording head, or to the conveying belt or the conveying drum, or to the sheet.
Further, with Conventional Example 1, there is also the disadvantage that the recording device becomes large.
In Conventional Examples 1 and 3, a belt is provided at a position facing the recording head (the nozzle surface) in order to convey the sheet (i.e., in order to ensure the position of the sheet). Therefore, the maintenance device cannot be disposed at that position, and a drawback arises in that a complex mechanism is needed in order to move both the recording head and the maintenance device.
Because maintenance is carried out by moving the recording head, dummy jetting cannot be carried out during continuous printing. The drawback arises that, at the time of dummy jetting, printing must be interrupted, and the produceability deteriorates.
A pushing device, which pushes (urges) the recording medium when the recording medium is conveyed, is generally provided. However, in Conventional Examples 1 through 3, there are cases in which the pushing forces (the urging forces) in the widthwise direction of the recording medium become unbalanced. As a result, problems may arise such as the recording medium moves at an incline such that the image is slanted, and wrinkles in the paper arise such that paper jamming occurs.
Moreover, in Conventional Examples 1 through 3, when the pushing device are structured so as to always abut conveying rollers, the pushing forces applied by the pushing device are about 5 to 30 [gf] each, and are therefore sufficiently small. However, the conveying roller, whose both end portions are held by bearings or the like, is usually a both-end supported beam structure. Therefore, in such a structure, flexure, although slight, arises due to the total pushing force of the pushing device. In order to reduce such flexure, it suffices to make the members thick and sturdy. However, this leads to the device becoming larger and more expensive. In addition, when dealing with a wider recording medium by increasing the number of urging members of the pushing device in order to more reliably transmit driving force from the conveying rollers to the recording medium, the flexure increases even more, which is a cause of an imbalance in the conveying. Therefore, the balance of the urging forces in the widthwise direction of the recording medium must be ensured by taking into consideration the way of urging of the pushing forces of the pushing device (i.e., the urging positions) and the flexure of the conveying roller. This leads to the device becoming more complex and expensive.
The designing of the conveying device is carried out by using the maximum width of recording media as a reference. Generally, it is possible to handle recording media of smaller sizes than that. When printing onto a recording medium of the maximum size, a balance of urging forces in the widthwise direction of the recording medium can be obtained. However, when a smaller-sized recording medium is conveyed by being aligned at an end portion (side registration), even if the pushing device were to be provided so as to have left-right symmetry, the recording medium would be conveyed in an unbalanced state with respect to the flexure of the conveying roller, and there would be the concern that slanted conveying and wrinkling of the sheet would arise.
In a case in which the recording medium is conveyed by the driving forces of conveying rollers being transmitted to the recording medium by the recording medium being pushed against the conveying rollers by pushing device, the recording medium which is positioned within the printing region is simultaneously nipped by plural pushing device and conveying rollers. Accordingly, even if the pushed state or the nipped state changes as the recording medium moves, the recording medium is nipped in a uniform state on average, and the moving speed is stable. However, when printing at the upstream-most recording head array starts, the majority of the recording medium is not being nipped, and as the recording medium moves, the entire recording medium is gradually nipped. The same situation arises also when the downstream-most recording head array finishes printing. These differences in the states of the recording medium (the pushing and the nipping of the recording medium) cause fluctuations in the moving speed of the recording medium, and are a deterrent to achieving good image quality.